1. Field of the Invention
The present invention relates to a controller and a control method for a driving source and, more specifically, to a technique for controlling a driving source such that a difference between an actually output torque and a target value set in accordance with an output shaft speed (number of rotations) of the driving source becomes smaller.
2. Description of the Background Art
Conventionally, an engine used as a driving source for a vehicle has been known. The engine is controlled such that torque in accordance with an accelerator position is output. The engine output torque is adjusted based on a throttle opening position, phase of an intake valve, amount of fuel injection, ignition timing and the like.
The torque to be output by the engine changes in accordance with the request by a driver and, in addition, the state of operation of engine itself, state of automatic transmission, and vehicle behavior. Therefore, it is difficult to set the throttle opening position, phase of intake valve, amount of fuel injection, ignition timing and the like directly from the accelerator position. Therefore, the throttle opening position, phase of intake valve, amount of fuel injection, ignition timing and the like are determined in accordance with a target value of output torque of the engine. The target output torque of the engine can be set in consideration of a parameter or parameters other than the accelerator position, such as the output shaft speed of the engine (see, for example, page 27 of Japanese Patent Laying-Open No. 2003-120349).
In a driving source control system, there is a dead time from the input of target value of output torque to the output of a command value of, for example, the ignition timing. Therefore, if the target output torque is set from the output shaft speed as described in Japanese Patent Laying-Open No. 2003-120349, there is a time lag from the output of target output torque until the output torque corresponding to the target value is attained. Therefore, the next target value may possibly be set using the output shaft speed that has not yet reflected the change corresponding to the target output torque set last time. This may lead to setting of a target value larger than necessary, or a target value smaller than necessary. As a result, the output torque of driving source becomes unstable.